The present invention is related to CRT information display systems and more particularly to color display stations (terminals) which are used in such display systems. The term "color" is used herein to designate multicolor capability of providing at least three distinct color hues.
Typically in CRT information display systems, a remote computer acts through a computer controlled control unit, which may be a microprocessor (MPU), to provide information and control signals to a CRT display station and this results in the production of a visual image on a CRT screen. For a color display information system such as the IBM 3270 system, the IBM control unit 3274 with IBM configuration support C, or its equivalent, if it identifies that it is connected to an appropriate IBM color display station such as a 3279, will initially transmit electrical convergence control signals to the display station since the convergence of the color beams in the IBM display station 3279 is controlled by electrical convergence signals received from the control unit. U.S. Pat. Nos. 4,203,051 and 4,203,054 relate to this convengence control system. After the control unit has transmitted these convergence control signals to the display station, and after the control unit has read back information concerning these signals to verify their receipt, then the control unit proceeds to transmit character display information to the display station wherein the character display information includes character attribute information such as the color of the character to be produced. Under some conditions extended attribute and color information is also provided to the display station if the control unit recognizes the display station as a color station having this capability.
The above identified system requires that the control unit transmits convergence data and that this data is subsequently read back to the control unit prior to the transmission of character display data and extended attribute data. If the electrical convergence signals are not properly read back by the control unit, the control unit will not implement any extended attribute characteristics and the control unit will cease to send display information and a desired visual display will not be provided.
In the display system described above, the convergence signals are stored in the display station since their presence is required to implement control of beam convergence circuitry located in the display station. In addition, provision is also made for operator adjustment of the stored convergence control signals so as to enable the operator to adjust the display station beam convergence. The entire operator convergence procedure is complex and tends to confuse operators of the display station. In addition, the operator convergence procedure is time consuming. Also extensive storage space must be provided in the display station for the convergence signals. For these reasons the present invention differs from the prior system in that it contemplates a preconverged CRT which utilizes factory preadjusted mechanical convergence control apparatus. This completely eliminates the need for the electrical convergence signals sent by the display system control unit. However, as previously noted, the receipt, storage, and subsequent read back of these convergence signals is still required for proper operation of the display system when a preconverged display station is used in an IBM 3270 system.
In addition, typically a multicolor visual display is only provided in prior systems if the multicolor display station receives display information data from a multicolor control unit.